Aeration is adopted to remove objectionable tastes and odour and also to remove the dissolved gases such as carbon dioxide, hydrogen sulphide etc. The iron and manganese present in water are also oxidised to some extent. This process is optional and is not adopted in cases where water does not contain objectionable taste and odour. Objectives : Aeration of water is done to accomplish the following objectives. 1. It removes tastes and odours caused by gasesdue to organic decomposition. 2. It increases the dissolved oxygen content of the water. 3. It removes hydrogen sulphide, and hence odour due to this is also removed.